Submersible pumping systems are often deployed into wells to recover petroleum fluids from subterranean reservoirs. Typically, the submersible pumping system includes a number of components, including one or more fluid filled electric motors coupled to one or more high performance pumps. Each of the components and sub-components in a submersible pumping system must be engineered to withstand the inhospitable downhole environment, which includes wide ranges of temperature, pressure and corrosive well fluids.
Components commonly referred to as “seal sections” protect the electric motors and are typically positioned between the motor and the pump. In this position, the seal section provides several functions, including transmitting torque between the motor and pump, restricting the flow of wellbore fluids into the motor, protecting the motor from axial thrust imparted by the pump, and accommodating the expansion and contraction of motor lubricant as the motor moves through thermal cycles during operation. Many seal sections employ seal bags to accommodate the volumetric changes and movement of fluid in the seal section. Seal bags can also be configured to provide a positive barrier between clean lubricant and contaminated wellbore fluid.
In the past, seal bags have been constructed by sliding an open-ended bag over cylindrical mounting blocks. As shown in the Prior Art drawing in FIG. 1, a prior art seal bag 10 includes a central portion 12 and two neck portions 14. The prior art seal bag 10 is installed over cylindrical mounting blocks 16 by fastening the open neck portions 14 to the cylindrical mounting blocks 16 with common hose clamps 18. This prior art design may be unsuitable in certain applications because the hose clamps 18 tend to shear the prior art seal bag 10 after repeated or extensive expansion. Furthermore, the necessity of the neck portions 14 in the prior art seal bag 10 decreases the available length and volume of the central portion 12.
As the use of downhole pumping systems extends to new applications, traditional bladder systems may fail under inhospitable downhole environments. For example, the use of downhole pumping systems in combination with steam assisted gravity drainage (SAGD) technology exposes bladder components to temperatures in excess of 500° F. To increase the resistance of the bladder to degradation under these increasingly hostile environments, manufacturers have employed durable polymers, including various forms of polytetrafluoroethylene (PTFE), as the preferred material of construction. Although PTFE is generally resistant to the harsh downhole environment, the use of PTFE as a material of construction is discouraged by the need to create the bladder with a seam-type design that frustrates efforts to provide an effective seal. There is, therefore, a need for an improved seal bag, seal sections and submersible pumping systems that overcome the deficiencies of the prior art. It is to this and other needs that the present invention is directed.